The present invention concerns a stereoselective enzymatic reductive amination process.
Robl in U.S. Pat. No. 5,508,272 disclose compounds of the formula 
wherein A is 
as possessing neutral endopeptidase and angiotensin converting enzyme inhibition activity. Among these compounds is [4S-[4xcex1(R*), 7xcex1, 10axcex2]]-octahydro-4-[(2-mercapto-1-oxo-3-phenylpropyl)amino]-5-oxo-7H-pyrido[2,1-b][1,3]thiazepine-7-carboxylic acid which is currently undergoing clinical evaluation.
Robl discloses that the amino lactam portion of this compound; i.e., the intermediate 
can be prepared by coupling an alkyl ester compound such as (S)-2-amino-6,6-dimethoxyhexanoic acid methyl ester with the N-protected amino acid 
wherein P1 is an amino protecting group and P2 is a sulfur protecting group to give the dipeptide of the formula 
Removal of the P2 protecting group, followed by acid catalyzed cyclization, and removal of the P1 protecting group gives [4S-(4xcex1, 7xcex1, 10axcex2)]-octahydro-4-amino-5-oxo-7H-pyrido[2,1-b][1,3]thiazepine-7-carboxylic acid, methyl ester.
Robl discloses preparing (S)-2-amino-6,6-dialkoxyhexanoic acid, alkyl ester, such as (S)-2-amino-6,6-dimethoxyhexanoic acid, methyl ester, by converting N-protected L-xcex5-hydroxynorleucine to its methyl ester, oxidizing to a corresponding aldehyde, such as of the formula 
then reacting with trimethyl orthoformate in the presence of a strong acid catalyst, and removing the P3 protecting group.
The present invention provides a process for the stereoselective enzymatic conversion of certain keto carboxylic acid derivatives to form the corresponding alkylamino acid compounds. The amino compounds prepared by the enzymatic process of the invention can be conveniently converted to the corresponding (S)-2-amino-6,6-dialkoxyhexanoic acid, alkyl ester or stable salts of such compounds such as phosphate, oxalate or bis salt with a compound such as N-(trifluoroacetyl)-L-homocysteine, (1xe2x86x921xe2x80x2)-disulfide.
More specifically, the present invention is directed to a process for preparing an alkylamino acid compound of the formula (formula I) 
wherein R1 is hydrogen or a monovalent cation or a C1-C18 alkyl (preferably C1-C10 alkyl, more preferably lower alkyl), R2 is a moiety of the formula 
a moiety of the formula 
wherein each R3 is a C1-C18 alkyl (preferably C1-C10 alkyl, more preferably lower alkyl); or a moiety of the formula 
wherein each R4 is H or R3 comprising contacting an alkylketo compound of the formula (formula II) 
wherein R2 is as defined above, and R1 is as defined above, with an amino acid dehydrogenase in the presence of ammonia and a co-factor under conditions suitable for formation of the compound of formula I.
The present invention also concerns an engineered yeast host cell containing recombinant nucleic acid capable of expressing a phenylalanine dehydrogenase enzyme and endogenous or recombinant nucleic acid capable of expressing a formate dehydrogenase enzyme.